Citation

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Abstract

In March and April, 2012, Geoscience Australia undertook a seabed characterisation survey, aimed at supporting the assessment
of CO2 storage potential of the Vlaming Sub-basin, Western Australia. The survey, undertaken as part of the National CO2
Infrastructure Plan program was targeted to provide an understanding of the link between the deep geological features of the
area and the seabed, and connectivity between them as possible evidence for seal integrity. Data was acquired in two sections
of the Rottnest Shelf lying above the regional seal - the South Perth Shale - and the underlying potentially CO2-suitable
reservoir, the Gage Sandstone. Seabed samples were taken from 43 stations, and included 89 seabed grab samples. A total of
653 km2 of multibeam and backscatter data was obtained. Chirper shallow sub-bottom profile data was acquired concurrently.
6.65 km2 of side-scan sonar imagery was also obtained. The two surveyed areas, (Area 1 and Area 2), are set within a shallow
sediment starved shelf setting. Area 2, situated to the southwest of Rottnest Island, is characterised by coralline red algal
(rhodolith) beds, with ridges and mounds having significant rhodolith accumulations. The geomorphic expression of structural
discontinuities outcropping at the seabed is evident by the presence of linear fault-like structures notable in Area 1, and
north-south trending lineaments in Area 2. North-south trending structural lineaments on the outer section of Area 2 have
in places, mounds standing 4-5 m above the seafloor in water depths of 80-85 m. Although there are apparent spatial correlations
between seabed geomorphology and the structural geology of the basin, the precise relationship between ridges and mounds that
are overlain by rhodolith accumulations, fluid seepage, and Vlaming Sub-basin geology is uncertain, and requires further work
to elucidate any links.